1. Field of the Invention
This invention relates in general to magnetic transducers, and more particularly to a method and apparatus for forming a symmetrical sensor structure for reducing electrical and magnetic noise.
2. Description of Related Art
Magnetic recording is a key and invaluable segment of the information-processing industry. While the basic principles are one hundred years old for early tape devices, and over forty years old for magnetic hard disk drives, an influx of technical innovations continues to extend the storage capacity and performance of magnetic recording products.
In the case of the magnetic hard disk drives, the areal density or density of written data bits on the magnetic medium has increased by a factor of more than two million since the first disk drive was applied to data storage. Since 1991, areal density has grown by the well-known 60% compound growth rate, and this is based on corresponding improvements in heads, media, drive electronics, and mechanics.
Magnetic recording heads have been considered the most significant factor in areal-density growth. The ability of these components to both write and subsequently read magnetically recorded data from the medium at data densities well into the Gbits/in2 range gives hard disk drives the power to remain the dominant storage device for many years to come.
Important features of the disk drives include a rotating magnetic disk, write and read heads that are mounted on a slider having an air-bearing surface (ABS), and a suspension arm for suspending the slider above the rotating disk. The read and write heads are connected to processing circuitry that implements the writing and reading functions.
In operation, an actuator swings the suspension arm to position the read and write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent the air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk.
Prior to 1991, magnetic heads were designed with a single inductive sensor for performing both reading and writing functions. However, the decreasing signal amplitude resulting from higher areal densities (e.g., 500 Mbits/in2 or greater) promoted the development of magnetoresistive (MR), and then giant-magnetoresistive (GMR) read sensors and tunneling magnetoresistive (TMR) sensors, which may all be combined with an inductive head. The inductive head thereafter typically performed the write function. Accordingly, the read sensor was designed with narrower gaps and pole geometries to accommodate write track widths that are typically wider than the corresponding read widths. Hence, the read sensor could remain entirely over a written track resulting in a higher signal to noise ratio.
However, with higher data densities, pole edge effects become more significant. As higher density recording media is used, the read sensor is built smaller to be capable of reading the high-density recording media. As the read sensor is reduced in size, small transient currents due to electrostatic discharge (ESD) are generated and can cause damage to the read sensors.
To prevent damage from the electrostatic discharge, electrical shield shunts are used to protect read sensors. Shield shunts for ESD protection are essentially purposeful shield shorts. These high resistance shield shunts allow accumulated charges to be slowly dissipated. Experimentally, the shield shunts have resulted in yield improvements during fabrication of the sensors.
Unfortunately, shield shunts will also couple unwanted electrical and magnetic noise from outside the file, passing the noise into the file through the shield shunts to the read sensor. The sensor typically picks up this noise; coupling it more to one sensor lead than to the other in the file. This unbalanced noise is difficult to eliminate and results in unwanted electrical and magnetic noise.
It can be seen then that there is a need to improve magnetic and electrical noise cancellation in read heads.